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L_0399 | the senses | DD_0159 | This diagram shows the anatomy of the human ear. The human ear is divided into the outer ear which contains the auricle and the earlobe. The outer ear is followed by the middle ear that contains eardrum and tympanic cavity and the ossicles. Lastly, the inner ear followed the middle ear and it contains the semicircular canals, vestibule, cochlea portions. The auditory canonical connects the outer ear to the middle ear. The eardrum and the tympanic cavity are at the end of the auditory canal. The vestibular nerve, semicircular ducts and cochlea are after the tympanic cavity. Ossicles are tiny bones in the middle ear that transmit sound from the eardrum to the cochlea. Sound waves travel through the outer ear, are modulated by the middle ear, and are transmitted to the inner ear. | image | teaching_images/human_system_ear_6103.png |
L_0405 | male reproductive system | DD_0164 | This image shows the posterior view of female reproductive system. The female reproductive system (or female genital system) is made up of the internal and external sex organs that function in human reproduction. The female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes, and to carry a fetus to full term. The internal sex organs are the uterus and Fallopian tubes, and the ovaries. The uterus or womb accommodates the embryo which develops into the fetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova (egg cells). The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris and vaginal opening. The vagina is connected to the uterus at the cervix. | image | teaching_images/human_system_reproductory_7014.png |
L_0405 | male reproductive system | DD_0165 | The diagram shows the parts and organs of the male reproductive system. The male reproductive organs include the penis, testes, epididymis, Ductus (vas) deferens, and prostate gland. The penis is an external, cylinder-shaped organ that contains the urethra. The urethra is the tube that carries urine out of the body. It also carries sperm out of the body. The testis (testis, singular) are oval organs that produce sperm and secrete testosterone. They are located inside a sac called the scrotum that hangs down outside the body. The scrotum also contains the epididymis. The epididymis is a tube that is about 6 meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum on top of the testes. The epididymis is where sperm mature. It stores the sperm until they leave the body. The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. Semen is a whitish liquid that contains sperm. It passes through the urethra and out of the body. Also shown are some parts of the digestive system like the rectum and anus. | image | teaching_images/human_system_reproductory_7036.png |
L_0405 | male reproductive system | DD_0166 | The diagram below shows the female reproductive system. The female reproductive system is made up of the internal and external sex organs that function in human reproduction. The internal sex organs are the uterus and Fallopian tubes, and the ovaries. The uterus or womb accommodates the embryo which develops into the fetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova (egg cells). The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris and vaginal opening. The vagina is connected to the uterus at the cervix. The uterus or womb is the major female reproductive organ. | image | teaching_images/human_system_reproductory_7039.png |
L_0407 | reproduction and life stages | DD_0167 | This diagram shows a blastocyst, which is a small, fluid-filled ball of cells that travels through the fallopian tube until it implants on the wall of the uterus and continues to develop as an embryo. The blastocyst is composed of an outer, circular layer and an internal mass. The outside is known as the trophoblast and looks like a single layer of cells. It will eventually develop into structures that support the developing fetus. The internal mass is called the inner cell mass, also known as the embryoblast. It will eventually develop into a fetus. | image | teaching_images/blastocyst_9028.png |
L_0407 | reproduction and life stages | DD_0168 | This diagram shows the six stages of development of a human embryo, in two rows that are arranged left to right. The first stage, at the top left, is a fertilized egg, which is a single cell. After fertilization, the egg undergoes mitosis, which replicates the cells so that the embryo can grow. The 2-, 4-, 8-, and 16-cell stages each show a progressively larger number of cells, seemingly arranged at random. The final stage is the blastocyst, where the cells appear to form a ball. After this, the embryo will implant on the wall of the uterus and be known as a fetus. | image | teaching_images/blastocyst_9024.png |
L_0407 | reproduction and life stages | DD_0169 | This diagram shows the blastocyst stage in the process of fertilization. The blastocyst has an inner and outer layer of cells. The inner layer is called the embryoblast, will develop into the new human being. The outer layer is called the trophoblast, will develop into other structures needed to support the new organism. This layer surrounds the inner cell mass or the embryoblast and a fluid-filled cavity known as the blastocoele. When the outer cells of the blastocyst embeds itself in the uterine lining or the endometrium. This process is called implantation. It generally occurs about a week after fertilization. | image | teaching_images/blastocyst_9033.png |
L_0415 | cycles of matter | DD_0175 | This diagram depicts the water cycle, which is an important part of the ecosystem. The water in the water cycle exists in three different phases, liquid, solid (ice) and gas (water vapor). Water from lakes and oceans evaporates and is carried by rising air currents in the atmosphere. In the atmosphere the water vapor condenses and forms tiny droplets of water that form clouds. When the droplets get big enough the water comes back to earth in the form of precipitation. Precipitation can be in the form of rain, snow, sleet, or hail. Eventually the water evaporates again and the cycle starts over. Water can also enter the atmosphere through trees and plants from a process called transpiration. | image | teaching_images/cycle_water_1490.png |
L_0415 | cycles of matter | DD_0176 | This diagram shows the processes of the water cycle. It takes place on, above, and below Earths surface. During the water cycle, water occurs in three different states: gas (water vapor), liquid (water), and solid (ice). Many processes are involved as water changes state to move through the cycle. One of the processes is called Evaporation. It takes place when water on Earths surface changes to water vapor. The sun heats the water and turns it into water vapor which escapes up into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation is another process takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration is yet another process that takes place when plants release water vapor through pores in their leaves called stomata. As the water vapor rises up into the earth's atmosphere, it cools and condenses. Condensation is the process of converting water vapor into water droplets. If the droplets get big enough, they fall as precipitation. Precipitation is any form of water that falls from the atmosphere. Precipitation that falls on land may flow over the surface of the ground. This water is called runoff. The runoff may reach a water body such as an ocean or get soaked into the ground. | image | teaching_images/cycle_water_1503.png |
L_0415 | cycles of matter | DD_0177 | This diagram shows the water cycle. Water from lakes, streams, rivers, and other bodies of water evaporates and turns into clouds. This leads to condensation which leads to precipitation in the form of rain and snow. Some precipitation adds to the bodies of water and some goes into the ground. The water that goes into the ground is called ground water--some of it eventually makes its way to bodies of water. Water also can come down from mountains and end up in bodies of water--this is called runoff. | image | teaching_images/cycle_water_4953.png |
L_0424 | photosynthesis | DD_0183 | This diagram depicts photosynthesis. Photosynthesis is the process in which plants synthesize glucose. The process uses carbon dioxide and water and also produces oxygen. The plant gets energy from sunlight using a green pigment called chlorophyll. Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose is used for energy by the cells of almost all living things. Plants make their own glucose. | image | teaching_images/photosynthesis_1262.png |
L_0424 | photosynthesis | DD_0184 | This diagram shows the process of photosynthesis, the process of how plants convert sunlight into energy. The plant uses sunlight and water to make glucose and creates oxygen as a waste product. Chemical energy is stored in the bonds of glucose molecules. | image | teaching_images/photosynthesis_4103.png |
L_0424 | photosynthesis | DD_0185 | This diagram represents photosynthesis. Photosynthesis the process in which plants synthesizes glucose. During photosynthesis, it gets its energy from the sun (light energy.) Photosynthesis changes light energy (the energy the plant receives from the sun) to chemical energy. This process uses carbon dioxide and water. In return, it produces oxygen and carbohydrates. It does this by the energy it receives from the sun. The equation for photosynthesis is 6CO2 + 6H2 O + Light Energy C6 H12 O6 + 6O2. | image | teaching_images/photosynthesis_4126.png |
L_0435 | history of life on earth | DD_0192 | The diagram is a representation of the major division of earths history. The geological timescale is a representation of time elapsed after the formation of earth, divided into slices, each differentiated by a geological event whose record is held in rock samples. Geological time is primarily divided into eons, which are divided into eras, which are further divided into periods. The periods are further divided into epochs, and epochs into ages, while eons are grouped into super-eons. The lengths of these eras are often measured by the term “mya,” which represents “millions of years ago. The first three eons are grouped under the Precambrian super-eon. The fourth eon, called the Phanerozoic, is ongoing. Although the first three eons together account for most of Earthas history, stretching out for nearly four billion years, there was little of note in terms of biological activity or geological diversity. So, in representations such as the table above, they are usually collectively called the Precambrian. It contains the Hadeon eon, when Earth was forming and the Late Heavy Bombardment took place; the Archeon eon, when water first showed up and the first lifeforms evolved; the Proterozoic eon, when the first multicellular organisms appeared and Earthas atmosphere received oxygen for the first time as a result of the proliferation of cyanobacteria. | image | teaching_images/geologic_time_6924.png |
L_0435 | history of life on earth | DD_0193 | The diagram shows an example of geologic time scale, which is a tool that scientists and historians used to describe and understand the different time frames of the Earths existence. This geologic time scale shows a timeline of events beginning from the late Proterozoic Era, approximately 650 million years ago. It is divided into eras and periods, and lists the major events that occurred in Earths history each period. From the geologic time scale, we can tell when different creatures evolved and first appeared on Earth. We know that the first amphibians appeared during the Devonian Period in the Paleozoic Era, approximately 400 million years ago. The first dinosaurs appeared during the Triassic Period of the Mesozoic Era, about 250 million years ago. Humans like us only appeared on Earth approximately 2.6 million years ago, during the Quaternary Period of the Cenozoic Era. The human race is very young, considering the Earth is approximately 4.6 billion years old! | image | teaching_images/geologic_time_6918.png |
L_0513 | excretion | DD_0201 | This is the diagram representing the human excretory system. The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, to help maintain internal chemical homeostasis and prevent damage to the body. It has following parts: The aorta begins at the top of the left ventricle, the heart's muscular pumping chamber. The inferior vena cava is a large vein that carries deoxygenated blood from the lower and middle body into the right atrium of the heart. The kidneys are bean-shaped organs which are present on each side of the vertebral column in the abdominal cavity. The kidney's primary function is the elimination of waste from the bloodstream by production of urine. The ureters are muscular ducts that propel urine from the kidneys to the urinary bladder. The urinary bladder is the organ that collects waste excreted by the kidneys prior to disposal by urination. Urethra is a tube which connects the urinary bladder to the outside of the body. | image | teaching_images/human_system_excretory_6107.png |
L_0513 | excretion | DD_0202 | This is a diagram of the major organs of the excretory system. The kidneys, ureter, bladder, and urethra all play important roles in this system. The kidneys filter blood and produce urine. The kidneys are shaped like beans and are located on each side of the body. After the kidneys, urine enters into the ureter. Then the urine moves into the bladder. When the bladder is about half full, it then releases into the urethra. This is how urine is filtered out of the body. | image | teaching_images/human_system_excretory_6117.png |
L_0513 | excretion | DD_0203 | The diagram shows the human urinary system. It includes two kidneys, two ureters and a urinary bladder. Blood is filtered by the kidneys to remove waste. Excess water and waste leaves the kidneys in the form of urine through the ureters to the bladder. Contractions of muscles in the ureters move the urine down into the bladder. Urine is excreted from the bladder through the urethra by the process of urination. | image | teaching_images/human_system_excretory_6115.png |
L_0719 | nuclear energy | DD_0204 | This Diagram shows how a Nuclear plant Work. Heat is used to boil water into steam and drive a turbine which turns a generator, making electricity. There are two separate water systems involved. One pumps fluid around the core of the reactor, absorbing the heat and keeping the pile from going into a meltdown. This liquid is kept separate because it's highly radioactive. It's pumped through carefully sealed pipes that go through a second water tank. The heat from the irradiated water heats these pipes, and then the pipes heat the second water tank, turning that water into steam. The steam is used to spin turbines, which are kind of like an RC car's motor except kind of opposite like, this generate electricity. The turbine water is clean and relatively safe, because it's not in direct contact with the irradiated systems. | image | teaching_images/nuclear_energy_7093.png |
L_0719 | nuclear energy | DD_0205 | Nuclear energy is the energy released in nuclear reactions. Two types of reactions that release huge amounts of energy are nuclear fission and nuclear fusion. The diagram demonstrates Nuclear Fusion. Nuclear fusion is a nuclear reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles (neutrons and/or protons). In the diagram, there are two hydrogen isotopes, Deuterium and Tritium. These combine to form a single, larger nucleus. They form a helium nucleus and a neutron. A great deal of energy is also released. | image | teaching_images/nuclear_energy_8115.png |
L_0719 | nuclear energy | DD_0206 | The diagram illustrates the process of Nuclear fission. Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a great deal of energy like heat and radiation from a very small amount of matter. Illustrated in the diagram is a neutron colliding with a uranium nucleus causing it to split into two smaller daughter nuclei. This process releases a large amount of energy and also releases three more fast neutrons. This type of reaction is used to create a chain reaction. If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. If a nuclear chain reaction is controlled, it produces energy more slowly. This is what occurs in a nuclear power plant. The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity. | image | teaching_images/nuclear_energy_8118.png |
L_0719 | nuclear energy | DD_0207 | This is how we get electricity from nuclear power. The water near the cooling towers is through the reservoir and then back up to a filter. The water then goes through the reactor core and turns into steam. The steam from the reactor then travels into the condenser and turbines were it then goes through the generator and produces electricity. | image | teaching_images/nuclear_energy_7101.png |
L_0722 | acceleration | DD_0208 | As time increases, distance increases as well. Over time, there is a steady speed and then a straight line indicates a stationary moment in time. It then returns to the start. | image | teaching_images/velocity_time_graphs_8216.png |
L_0722 | acceleration | DD_0209 | Figure 1 presents different velocity-time graphs. A velocity-time graph shows how an object's velocity or speed changes over time. The y axis represents velocity (v), while the x axis represents time (t). In the graph for constant velocity, the line remains horizontal, showing that the velocity of the object does not change over time. In the graph for constant acceleration, the line slopes upwards, showing that the velocity of the object increases over time. This increase in velocity is called acceleration. In the graph for constant retardation, the line slopes downwards, which means that velocity decreases over time. This decrease is called retardation. Retardation can also be called negative acceleration or deceleration. A moving object can both accelerate and decelerate. In the graph for irregular motion, the line moves up and down. This means that the velocity of object increases and decreases several times. | image | teaching_images/velocity_time_graphs_8213.png |
L_0722 | acceleration | DD_0210 | This Diagram shows a Velocity-time that is used for determine the acceleration of an object. The vertical axis of a velocity-time graph is the velocity of the object and the horizontal axis is the time taken from the start. When an object is moving with a constant velocity, the line on the graph is horizontal. When an object is moving with a steadily increasing velocity, or a steadily decreasing velocity, the line on the graph is straight, but sloped. The diagram shows some typical lines on a velocity-time graph. The steeper the line, the more rapidly the velocity of the object is changing. The blue line is steeper than the red line because it represents an object that is increasing in velocity much more quickly than the one represented by the red line. | image | teaching_images/velocity_time_graphs_8220.png |
L_0734 | simple machines | DD_0211 | Shown in the diagram are the six types of simple machines. A simple machine is a mechanical device that makes work easier. It includes the inclined plane, wedge, lever, wheel and axle, screw and pulley. An inclined plane is a flat surface that is slanted, or inclined, so it can help move objects across distances. A common inclined plane is a ramp used to lift heavy objects in a back of a truck. Instead of using the smooth side of the inclined plane to make work easier, you can also use the pointed edges to do other kinds of work. When you use the edge to push things apart, this movable inclined plane is called a wedge. An ax blade is one example of a wedge. Any tool that pries something loose is a lever. Levers can also lift objects. A lever is an arm that turns against a fulcrum (the point or support on which a lever pivots). Think of the claw end of a hammer that you used to pry nails loose; it's a lever. The Wheel and Axle makes work easier by moving objects across distances. The wheel (or round end) turns with the axle (or cylindrical post) causing movement. On a wagon, for example, a container rests on top of the axle to help transport heavy objects. A Screw helps you do work is that it can be easily turned to move itself through a solid space like turning a jar cover to keep it the jar air tight. Instead of an axle, a wheel could also rotate a rope, cord, or belt. This variation of the wheel and axle is the pulley. In a pulley, a cord wraps around a wheel. Instead of an axle, you can use the wheels rotation to raise and lower objects, making work easier. On a flagpole, for example, a rope is attached to a pulley to raise and lower the flag more easily. | image | teaching_images/simple_machines_9246.png |
L_0740 | transfer of thermal energy | DD_0212 | This diagram shows convection currents. Convection is the transfer of heat from one place to another by the movement of fluids. The heat source lies at the bottom of the diagram. The heat generated by this source causes the air next to it, to warm up. Warm air is lighter than cool air, and hence it rises up. As it rises up, it moves away from the heat source and cools down. As it cools down, it gets heavier and sinks towards the heat source. This cycle continues and causes a convection current. | image | teaching_images/convection_of_air_8050.png |
L_0740 | transfer of thermal energy | DD_0213 | This diagram shows the phenomena of the transfer of thermal energy. It happens by the convection of hot and cold air. The sun heats up the air, making it warm and less dense. Less dense air tends to go up, cooling down as doing it. Cool air becomes more dense and tends to sink, and wind does the job of making the air travel through different places, warming or cooling as he goes. | image | teaching_images/convection_of_air_6657.png |
L_0743 | measuring waves | DD_0214 | The figure shows a transverse wave. In a transverse wave, wave amplitude is the height of each crest above the resting position. The higher the crests are, the greater the amplitude. Another important measure of wave size is wavelength. Wave amplitude is the maximum distance the particles of a medium move from their resting position when a wave passes through. The resting position (dotted line in the middle of the wave) is where the particles would be in the absence of a wave. Wavelength can be measured as the distance between two adjacent crests of a transverse wave. It is usually measured in meters. Wavelength is related to the energy of a wave. Short-wavelength waves have more energy than long-wavelength waves of the same amplitude. | image | teaching_images/waves_9296.png |
L_0743 | measuring waves | DD_0215 | This diagram represents a sound wave and its characteristics. The peak of a wave is called compression or crest. The valley of a wave is called rarefaction or trough. Wave length is the length between two consecutive peaks, i.e. crest or two consecutive valleys, i.e. trough of a wave. Louder sound has shorter wavelength and softer sound has longer wavelength. Magnitude of maximum disturbance on either side of the normal position or mean value in a medium is called amplitude. In other words, amplitude is the distance from normal to the crest or trough. Time required to produce one complete wave is called time period or time taken to complete on oscillation is called the time period of the sound wave. The number of sound waves produced in unit time is called the frequency of sound waves. Frequency is the reciprocal of the time period of wave. Distance covered by sound wave in unit time is called the velocity of sound wave. | image | teaching_images/waves_7678.png |
L_0753 | the electromagnetic spectrum | DD_0216 | This diagram shows light waves of varying lengths, and some of their characteristics. The red line illustrates the wavelengths. Above that is a bar showing which light waves penetrate the Earth's atmosphere. Below the red line are the names of the different types of light, with their wavelength measured in (m). The illustrations of physical objects are to show scale. Below that is a diagram of the different light frequencies, measured in Hertz. Below that is a measure of the temperatures at which these light waves are most commonly emitted. | image | teaching_images/em_spectrum_6818.png |
L_0753 | the electromagnetic spectrum | DD_0217 | The diagram shows different kinds of waves. Visible light is the part of the electromagnetic spectrum that humans can see. Visible light includes all the colors of the rainbow. Each color is determined by its wavelength. Visible light ranges from violet wavelengths of 400 nanometers (nm) through red at 700 nm. There are parts of the electromagnetic spectrum that humans cannot see. This radiation exists all around you. You just can't see it! Every star, including our Sun, emits radiation of many wavelengths. Astronomers can learn a lot from studying the details of the spectrum of radiation from a star. Many extremely interesting objects can't be seen with the unaided eye. | image | teaching_images/em_spectrum_9095.png |
L_0755 | optics | DD_0218 | This diagram explains the concept of refraction. Light travels at a constant speed in vaccuum but travels at different speends in different media. When light travels from one medium to another, the speed of light changes causing it to appear to bend. This bending of light is called refraction. Refraction occurs when the angle of incidence (i) is not 90 degrees. In this diagram (r) is the angle of refraction. The angle of refraction is dependent on the angle o incidence as well as the speed of light in the medium through which it is travelling. XY is the boundary between the media through which light is travelling. At the point of incidence where the ray strikes the boundary XY, a line can be drawn perpendicular to XY. This line is known as a normal line (labeled NN' in the diagram). | image | teaching_images/optics_refraction_9190.png |
L_0755 | optics | DD_0219 | This diagram shows the setup of an amateur reflecting telescope. The telescope tube sits on a movable mount that allows it to point at and track objects in the sky. The mount shown is equitorial, meaning that it can be aligned to the north star for easier tracking of other stars and planets as they move ac cross the sky. The mount has a counterweight to help balance the weight of the telescope tube. The entire assembly sits on the three legs of a tripod. When pointed at the sky, light enters the optical tube through its aperture. The aperture is the circular end of the tube that allows light to enter when uncovered. Once light has entered the telescope, it is gathered and directed to the eyepiece by mirrors. The lenses in the eyepiece take this light and bring an image to focus for a human to see. The finderscope is a second smaller telescope attached the optical tube. It has lower magnification than the telescope, and this makes finding objects and pointing the telescope easier. | image | teaching_images/parts_telescope_8149.png |
L_0755 | optics | DD_0220 | This diagram explains the law of reflection and shows how light gets reflected from a surface. The law of reflection states that the angle of incidence (i) is always equal to the angle of reflection (r). The angles of both reflected and incident ray are measured relative to the imaginary dotted-line, called normal, that is perpendicular (at right angles) to the mirror (reflective surface). On the other hand, Refraction is caused by the change in speed experienced by a wave when it changes medium. The refracted ray is a ray (drawn perpendicular to the wave fronts) that shows the direction that light travels after it has crossed over the boundary. The angle that the incident ray makes with the normal line is referred to as the angle of incidence. Similarly, the angle that the refracted ray makes with the normal line is referred to as the angle of refraction. Thus, this is what the following diagram is all about. | image | teaching_images/optics_refraction_9200.png |
L_0755 | optics | DD_0221 | The diagram below is about two different types of lens. A lens is a transparent piece of glass or plastic with at least one curved surface. A lens works by refraction: it bends light rays as they pass through it so they change direction. In a convex lens (sometimes called a positive lens), the glass (or plastic) surfaces bulge outwards in the center giving the classic lentil-like shape. A convex lens is also called a converging lens because it makes parallel light rays passing through it bend inward and meet (converge) at a spot just beyond the lens known as the focal point Convex lenses are used in things like telescopes and binoculars to bring distant light rays to a focus in your eyes. A concave lens is exactly the opposite with the outer surfaces curving inward, so it makes parallel light rays curve outward or diverge. That's why concave lenses are sometimes called diverging lenses. (One easy way to remember the difference between concave and convex lenses is to think of concave lenses caving inwards). Concave lenses are used in things like TV projectors to make light rays spread out into the distance. | image | teaching_images/optics_lense_types_9163.png |
L_0755 | optics | DD_0222 | This diagram shows the arrangement of optics found in a refracting telescope. Llight entering the telescope first encounters the large objective lens placed a telescopes aperture the optical tube through its aperture, a circular opening at the forward end of the tube. The objective lens is convex, and it causes rays of light entered the telescope parallel to one another to converge. The eyepiece lens is located in the path of these converging rays, and brings an image to focus for the human eye. | image | teaching_images/parts_telescope_8156.png |
L_0755 | optics | DD_0223 | This Diagrams shows the different types of lenses. A lens is a clear (transparent) object (like glass, plastic or even a drop of water) that changes the way things look by bending the light that goes through it. They may make things appear larger, smaller, or upside-down. Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses. If the lens is biconvex or plano-convex, a collimated beam of light passing through the lens converges to a spot (a focus) behind the lens. In this case, the lens is called a positive or converging lens. | image | teaching_images/optics_lense_types_9159.png |
L_0755 | optics | DD_0224 | This diagram shows the arrangement of optics found in a reflecting telescope. Light enters the optical tube through its aperture, a circular opening at the forward end of the tube. When light enters the telescope, it encounters a concave reflecting mirror at the back of telescope tube. This large reflecting mirror is called the objective. Light reflected from the objective converges on a small right angle mirror at the center of the optical tube. This mirror reflects the gathered light to the eyepiece. The lenses in the eyepiece take this light and bring an image to focus for a human to see. | image | teaching_images/parts_telescope_8153.png |
L_0762 | earth as a magnet | DD_0230 | This Diagram shows the Earth's Magnetic Field. Our planets magnetic field is believed to be generated deep down in the Earths core. And is created by the rotation of the Earth and Earth's core. It shields the Earth against harmful particles in space. The field is unstable and has changed often in the history of the Earth. The magnetic field creates magnetic poles that are near the geographical poles. A compass uses the geomagnetic field to find directions. Many migratory animals also use the field when they travel long distances each spring and fall. The magnetic poles will trade places during a magnetic reversal. | image | teaching_images/earth_magnetic_field_6775.png |
L_0762 | earth as a magnet | DD_0231 | This Diagram Shows the earth and how it acts as a magnet. It clearly depicts the geographic north pole and the magnetic north pole. Like all magnets, Earth has a magnetic field. Earths magnetic field is called the magnetosphere. It is a huge region that extends outward from Earth for several thousand kilometers but is strongest at the poles. Evidence in rocks shows that Earths magnetic poles switched positions hundreds of times in the past. Scien- tists think that Earths magnetic field is caused by the movement of charged particles through molten metals in the outer core. Earths magnetic field helps protect Earths surface and its organisms from harmful solar particles by pulling most of the particles toward the magnetic poles. Earths magnetic field is also used for navigation by humans and many other | image | teaching_images/earth_magnetic_field_6788.png |
L_0772 | inside the atom | DD_0241 | This diagram shows the makings of an atom. The nucleus contains protons and neutrons, which are represented as green and orange spheres. Protons have positive charges and neutrons have no charge. The rings outside the nucleus contain electrons, which have negative charges. The electrons are represented by purple spheres. The atom's mass is made up of the protons and neutrons. The outermost ring of electrons is called the valence ring, which contains one valence electron in this diagram. | image | teaching_images/atomic_structure_9020.png |
L_0772 | inside the atom | DD_0242 | Carbon has three isotopes which are shown in this diagram. Carbon always has six protons, but the number of neutrons it has can vary. The number of positively charged protons in an isotope is called the atomic number. The mass number of an isotope is equal to the number of its positively charged protons plus the number it's of neutrally charged neutrons. A Carbon-12 atom has six protons and six neutrons in its nucleus. A Carbon-13 isotope has six protons and seven neutrons in its nucleus, giving it a mass number of thirteen. Tritium has a proton and two neutrons in its nucleus, giving it a mass number of three. All three have a single electron. Another isotope of carbon, Carbon-14 has six protons and eight neutrons in its nucleus, giving it a mass number of fourteen. | image | teaching_images/isotopes_9127.png |
L_0772 | inside the atom | DD_0243 | Three isotopes of hydrogen are shown here. The number of protons in an atom determines the element, but the number of neutrons the atom of an element has can vary. The number of positively charged protons in an isotope is called the atomic number. This will also equal the number of electrons in a neutrally charged atom. The mass number of an isotope is equal to its atomic number plus the number of neutrally charged neutrons it has. A hydrogen atom has one proton and zero neutrons in its nucleus. Hyrogen has two isotopes called deuterium and tritium. Deuterim has a proton and a neutron in its nucleus, giving it a mass number of two. Tritium has a proton and two neutrons in its nucleus, giving it a mass number of three. All three have a single electron. | image | teaching_images/isotopes_7057.png |
L_0772 | inside the atom | DD_0244 | The figure shows the nuclear symbol for the chemical element Boron. There are two important numbers in a nuclear symbol. In the lower left part, there is the atomic number. The atomic number shows the number of protons. In the upper left part, there is the mass number. The mass number is the sum of the number of protons and neutrons. In addition, if the element is an ion, the charge is shown in the upper right part of the symbol. | image | teaching_images/atomic_mass_number_9001.png |
L_0772 | inside the atom | DD_0245 | The diagram shows how elements are written in relation to the mass and atomic number. The symbol X stands for the chemical symbol of the element. Two numbers are commonly used to distinguish atoms: atomic number and mass number. The symbol A at the top right of the element symbol refers to the mass number. Mass number is the number of protons plus the number of neutrons in an atom. The symbol Z at the bottom right of the element symbol refers to the atomic number. The atomic number is the number of protons in an atom. This number is unique for atoms of each kind of element. | image | teaching_images/atomic_mass_number_9009.png |
L_0772 | inside the atom | DD_0246 | The figure shows a diagrammatic representation of a Helium-4 atom. We see how the atom has a nucleus surrounded by shells of electrons. In this case, the atom has two protons and two neutrons in the central nucleus. Two electrons orbit around the nucleus. The electrons are both in the first shell. The protons have a positive charge. The electrons have a negative charge. The neutrons do not have a charge. | image | teaching_images/atomic_mass_number_9006.png |
L_0772 | inside the atom | DD_0247 | This diagram shows a simple model of an atom. At the center of the atom is the nucleus. The nucleus contains neutrons and protons. A proton is a particle with a positive electric charge. The neutron is a particle with no electric charge. Electrons are particles with negative charges. They revolve around the nucleus in orbits. An atom typically has the same number of protons and electrons. Hence the positive and negative charges cancel each other out. | image | teaching_images/atomic_structure_6540.png |
L_0772 | inside the atom | atomic_structure_9018 | This image shows the electron shells of a Germanium atom. There are a totals of 32 orbiting electrons in four distinct shells. The inner shell has two electrons. The second shell has 8 electrons. The third shell has 18 electrons. The fourth, outer shell has 4 electrons. The electrons in the outer shell are called valence electrons. In the center of the atom sits the nucleus. The nucleus has a positive charge. | image | teaching_images/atomic_structure_9018.png |
L_0775 | how elements are organized | DD_0249 | Pictured below is a diagram of the periodic table. The periodic table is used today to classify elements. The elements in a periodic table are organized by the atomic number. The number of protons in an atom is what the atomic number represents on the chart. Rows on the periodic table are called periods. The columns in the periodic table are called groups. The modern periodic table have 18 groups. The elements are arranged in the periodic table by the atomic number from left to right from the lowest atomic numbers to highest. | image | teaching_images/periodic_table_8162.png |
L_0775 | how elements are organized | DD_0250 | This image shows the Periodic table. It is a table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns. This ordering shows periodic trends, such as elements with similar behaviour in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right. The rows of the table are called periods; the columns are called groups. The periodic table provides a useful framework for analyzing chemical behaviour, and is widely used in chemistry and other sciences. | image | teaching_images/periodic_table_8157.png |
L_0775 | how elements are organized | DD_0251 | The following image shows the Periodic Table of Elements. This is a list of known atoms. In the table, the elements are placed in the order of their atomic numbers starting with the lowest number. The atomic number of an element is the same as the number of protons in that particular atom. In the periodic table the elements are arranged into periods and groups. A row of elements across the table is called a period. Each period has a number: from 1 to 7. Period 1 has only 2 elements in it: hydrogen and helium. Period 2 and Period 3 both have 8 elements. Other periods are longer. The periodic table can be used by chemists to observe patterns, and relationships between the elements. | image | teaching_images/periodic_table_7388.png |
L_0778 | introduction to chemical bonds | DD_0252 | Water is a transparent common substance that makes up the earth's oceans, lakes, seas, rivers, streams and more. Water is essential for every living thing to replenish and hydrate. The chemical formula for water contains one oxygen atom to two hydrogen atoms. Everything from the earth's crust to the human brain contain great amounts of water. Water on earth is continually being used and then goes through the water cycle to become new and usable again. The water cycle involves evaporation, transpiration, condensation, precipitation and runoff. Even though water does not have any calories or nutritional benefit it is essential to all living forms on earth. Fishing which occurs in salt and fresh type waters yields much food for the world's people. Water even involves exercise for those who like to swim and engage in other sports like water skiing, wakeboarding and so on. | image | teaching_images/lewis_dot_diagrams_9146.png |
L_0778 | introduction to chemical bonds | DD_0253 | This image shows the chemical structure of Acetylene. Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carboncarbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180. | image | teaching_images/lewis_dot_diagrams_9130.png |
L_0778 | introduction to chemical bonds | DD_0254 | The diagram shows the Lewis Dot Structure of Carbon. Lewis Structures are visual representations of the bonds between atoms and illustrate the lone pairs of electrons in molecules. The electrons in the outermost electron shell are called valence electrons. These electrons have an essential role in chemical bonding. Lewis Structures can also be called Lewis dot diagrams and are used as a simple way to show the configuration of atoms within a molecule. In constructing a Lewis Structure, an element is represented by a Lewis symbol (e.g. C for Carbon). It is surrounded by dots that are used to represent the valence electrons of the element. Lewis symbols differ slightly for ions. When forming a Lewis symbol for an ion, the chemical symbol is surrounded by dots that are used to represent valence electrons, and the whole structure is placed in square brackets with superscript representing the charge of the ion. | image | teaching_images/lewis_dot_diagrams_9140.png |
L_0779 | ionic bonds | DD_0255 | This diagram shows the ionic bonds in lithium fluoride molecule. An ionic bond is the force of attraction that holds together positive and negative ions. The lithium fluorine molecule consists of one lithium atom and one fluorine atom with the chemical formula of LiF. The lithium ion has one more protons than the number of electron thus has the charge of +1. The fluorine ion has one more electron than the number of protons thus has the charge of -1. The lithium ion and fluorine ion have equal but opposite charges so they attract each other. By the attracting force, they form a lithium fluoride molecule. | image | teaching_images/chemical_bonding_ionic_9071.png |
L_0779 | ionic bonds | DD_0256 | The diagram shows an example of ionic bonding. Ionic bonding is a type of chemical bond that occurs between a metallic atom and a nonmetallic atom that join together to form an ionic compound. In the figure, the metallic atom is the sodium atom and the nonmetallic atom is the chlorine atom. During iconic bonding, the metallic atom gives up an electron to the nonmetallic atom. The sodium atom therefore loses an electron while the chlorine atom gains an electron. Because of the electron transfer, each atom now has an unequal number of electrons and protons, thereby becoming an electrically charged ion. An atom that has lost an electron becomes an ion with a positive charge. A positive ion is called a cation. An atom that has gained an electron becomes an ion with a negative charge. A negative ion is called an anion. In short, the sodium atom becomes a sodium cation, whereas the chlorine atom becomes a chloride anion. (Chlorine becomes chloride when it gains an electrical charge.) Because the two ions have opposite electrical charges, they become attracted to each other and bond together, forming the ionic compound sodium chloride. | image | teaching_images/chemical_bonding_ionic_9066.png |
L_0780 | covalent bonds | DD_0257 | This diagram depicts covalent bonds in the ammonia compound. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It has 3 hydrogen atoms and 1 nitrogen atom. The nitrogen atom has 5 outer electrons, and the hydrogen atom has 1 electron. The nitrogen atom shares 2 electrons with each hydrogen atom, one provided by the nitrogen atom and the other provided by the hydrogen atom. | image | teaching_images/chemical_bonding_covalent_9051.png |
L_0780 | covalent bonds | DD_0258 | This diagram shows the covalent bonds in water molecule. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The water molecule consists of two hydrogen atoms and one oxygen atom with the chemical formula of H2O. The oxygen atom has 6 electrons and each hydrogen atom has one electron. The oxygen atom shares 2 electrons with two electrons from two hydrogen atoms. So, it completes the outer most shell of oxygen atom with 8 total electrons. | image | teaching_images/chemical_bonding_covalent_9053.png |
L_0780 | covalent bonds | DD_0259 | This diagram shows the covalent bonds in carbon dioxide molecule. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The carbon dioxide molecule consists of two oxygen atoms and one carbon atom with the chemical formula of CO2. At the outer most shell of carbon atom, there are 4 electrons. Each oxygen atoms shares 2 electrons with carbon atom. So, it completes the outer most shell of carbon atom with 8 total electrons. | image | teaching_images/chemical_bonding_covalent_9063.png |
L_0787 | hydrocarbons | DD_0260 | The diagram shows the chemical composition of four saturated hydrocarbons. It shows the chemical structure of four alkanes namely ethane, propane, butane and pentane with 2,3,4 and 5 carbon atoms respectively. All the above mentioned alkanes are straight chain compounds with 6,8,10 and 12 hydrogen atoms respectively. | image | teaching_images/hydrocarbons_7051.png |
L_0787 | hydrocarbons | DD_0261 | The diagram shows the molecular structure of Butane. Butane molecules have four carbon atoms and ten hydrogen atoms (C4 H10). Butane is classified as compounds that contain only carbon and hydrogen molecules, called Hydrocarbons. Saturated Hydrocarbons are the simplest Hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen atoms as possible and single bonds between carbon atoms. In other words, the carbon atoms are saturated with hydrogen. The diagram shows 3 carbon-carbon bonds and 10 carbon-hydrogen bonds. Their most important use is as fuels. Hydrocarbons are also used to manufacture many products, including plastics and synthetic fabrics such as polyester. | image | teaching_images/hydrocarbons_9121.png |
L_0787 | hydrocarbons | DD_0262 | The diagram shows the molecular structure of Hydrocarbons. Hydrocarbons can be classified into Saturated and Unsaturated Hydrocarbons. Saturated Hydrocarbons are the simplest Hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen atoms as possible and single bond between carbon atoms. In other words, the carbon atoms are saturated with hydrogen. As shown in the diagram, each carbon atoms are bonded to 3 hydrogen atoms and only one carbon atoms. In unsaturated hydrocarbons, The carbon atoms may have more than one bond to other carbon atoms and only 2 hydrogen atoms. Hydrocarbons are used to manufacture many products, including plastics and synthetic fabrics such as polyester. They are also used as fuels like Butane. | image | teaching_images/hydrocarbons_9118.png |
L_0789 | biochemical reactions | DD_0263 | The diagram depicts the process of cellular respiration. There are three steps in this process. The first step is Glycolysis. In Glycolysis, glucose in the cytoplasm is broken into two molecules of pyruvic acid and two molecules of ATP by direct synthesis. Then pyruvate from Glycolysis is actively pumped into mitochondria. One carbon dioxide molecule and one hydrogen molecule are removed from the pyruvate (called oxidative decarboxylation) to produce an acetyl group, which joins to an enzyme called CoA to form acetyl CoA. This is essential for the Krebs cycle.2 Acetyl CoA gives 2 NADH molecules and acetyl-CoA enters the Citric Acid Cycle, which is also known as Kreb's cycle. This happens inside the mitochondria. The citric acid cycle is an 8-step process involving different enzymes and co-enzymes. During the cycle, acetyl-CoA (2 carbons) + oxaloacetate (4 carbons) yields citrate (6 carbons), which is rearranged to a more reactive form called isocitrate (6 carbons). Isocitrate is modified to become -ketoglutarate (5 carbons), succinyl-CoA, succinate, fumarate, malate, and, finally, oxaloacetate. The total yield from 1 glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH2, and 2 ATP. All the hydrogen molecules which have been removed in the steps before (Krebs cycle, Link reaction) are pumped inside the mitochondria using energy that electrons release. Eventually, the electrons powering the pumping of hydrogen into the mitochondria mix with some hydrogen and oxygen to form water and the hydrogen molecules stop being pumped. Eventually, the hydrogen flows back into the cytoplasm of the mitochondria through protein channels. As the hydrogen flows, ATP is made from ADP and phosphate ions. The Electron transport Chain gives about 34 ATP by ATP synthase. The maximum energy generated per glucose molecule is 38 ATP. | image | teaching_images/cellular_respiration_9048.png |
L_0789 | biochemical reactions | DD_0264 | This diagram shows the biochemical reaction cycles. Since all energy source of the biological objects on the earth is the sun, the cycle starts from the sun. Sun gives light to plants. The plants produce Glucose or sugar and oxygen by the process called photosynthesis with carbon dioxide and water produced by other plants and animals. Specifically, the Chloroplasts in the plants produces the Glucose. The Glucose and the sugar and oxygen are consumed by other plants and animals by cellular respiration in mitochondria. By the cellular respiration, plants and animals produce ATP which is a source of energy. Comsuming the Glucose and oxygen, the plants and animals also produce water and carbon dioxide. The water and carbon dioxide provides the ingredient for photosynthesis of plants. With the water and carbon dioxide, the plants produces glucose and oxygen with sunlight which completes the cycle. | image | teaching_images/cellular_respiration_8026.png |
L_0789 | biochemical reactions | DD_0265 | The diagram depicts the Oxygen Cycle. This is the cycle that maintains the levels of oxygen in the atmosphere. Oxygen from the atmosphere is used up in two processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. Carbon dioxide and water are taken up by plants in the presence of sunlight and chlorophyll to give glucose and oxygen. This glucose and oxygen are converted into carbon dioxide and water during respiration. Respiration also gives energy for work in the form of ATP. | image | teaching_images/cellular_respiration_9045.png |
L_0936 | law of reflection | DD_0266 | This diagram shows Ray (optics). In optics, a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wave fronts of the actual light, and that points in the direction of energy flow. Rays are used to model the propagation of light through an optical system by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing. This allows even very complex optical systems to be analyzed mathematically or simulated by computer. All three rays should meet at the same point. The Principal Ray or Chief Ray (sometimes known as the b ray) in an optical system is the meridional ray that starts at the edge of the object and passes through the center of the aperture stop. This ray crosses the optical axis at the locations of the pupils. As such, chief rays are equivalent to the rays in a pinhole camera. The Central Ray is perpendicular to Infrared Radiation. The third one, called the Focal Ray, is a mirror image of the parallel ray. The focal ray is drawn from the tip of the object through (or towards) the focal point, reflecting off the mirror parallel to the principal axis. | image | teaching_images/optics_ray_diagrams_9167.png |
L_0936 | law of reflection | DD_0267 | This diagram explains the law of reflection and shows how light gets reflected from a surface. The law of reflection states that the angle of incidence (i) is always equal to the angle of reflection (r). The angles of both reflected and incident ray are measured relative to the imaginary dotted-line, called normal, that is perpendicular (at right angles) to the mirror (reflective surface). | image | teaching_images/optics_reflection_9179.png |
L_0936 | law of reflection | DD_0268 | The reflection of a tree shines in to the lake. When the human eye sees the reflection from the tree on the water it looks the right direction. The image of the tree is upside down. The water reflection on the lake makes things upright to the human eye. | image | teaching_images/optics_ray_diagrams_9168.png |
L_0936 | law of reflection | DD_0269 | This diagram depicts how light rays can reflect off various surfaces. Incident rays will reflect back at a specific angle if the surface is smooth. A rough or broken surface will have reflected rays with a wide variety of reflected angles. The left part of the diagram shows why your reflection in a mirror is smooth and natural looking. | image | teaching_images/optics_reflection_9183.png |
L_0972 | nucleic acid classification | DD_0270 | The diagram shows the structure of deoxyribonucleic acid (DNA) which carries the genetic information of organisms. DNA is made up of a double helix of two complementary strands. The strands of the double helix are anti-parallel with one being 5' to 3', and the opposite strand 3' to 5'. Each single strand of DNA is a chain of four types of nucleotides. The four types of nucleotide correspond to the four nucleobases adenine, cytosine, guanine, and thymine, commonly abbreviated as A, C, G and T. Adenine pairs with thymine (two hydrogen bonds), and guanine pairs with cytosine (three hydrogen bonds). During DNA replication, the parent DNA unwinds and each parental strand serves as a template for replication of new strands. Nucleobases are matched to synthesize the new daughter strands. | image | teaching_images/dna_6763.png |
L_0972 | nucleic acid classification | DD_0271 | This diagram shows the structure of a DNA or deoxyribonucleic acid. Deoxyribonucleic acid is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. Most DNA molecules consist of two strands coiled around each other to form a double helix. The two DNA strands are composed of simpler units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing compounds either cytosine (C), guanine (G), adenine (A), or thymine (T). The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. | image | teaching_images/dna_8052.png |
L_1063 | vision and the eye | DD_0272 | The ability to see is called vision. The eyes sense light and form images which The brain then interprets. The images are formed by the eyes and the brain tells us what we are looking at. All creatures have different types of eyes, some are great at seeing vast distances such as the eagle or owl and some are able to pick up light in dark settings in order to see better at night, such as cats. Many people have issues with their vision but we have been able to correct this with lenses which come in the form of glasses or contact lenses. The eyes are made up of several parts the pupil, cornea, iris, lens, retina and the optic nerve which carries the images the eyes sees and takes the images to brain for it to interpret. | image | teaching_images/human_system_eye_2857.png |
L_1063 | vision and the eye | DD_0273 | Below is a diagram of the structure of the eyeball. As you can see below, the eyeball is made up of various parts. One of the major parts is the cornea. The cornea of the eyeball is a clear covering that protects the eyeball. The light first comes through the cornea then goes through the pupil. The pupil is the opening in the center of the eyeball. The pupil is the dark part in the center of the iris, which is the colored part of the eye. The light then goes through the lens and reaches the retina. The retina is the part where the image first occurs. Then the optic nerves carries the impulses to the brain. | image | teaching_images/human_system_eye_6138.png |
L_1063 | vision and the eye | DD_0274 | This picture shows the parts of the eye. The light enters the eye through the pupil. The cornea covers the eye and protects it from damage. The iris controls the size of the pupil. The size of the pupil changes based on the amount of light that enters the eye. The lens projects the image onto retina. The retina has nerve cells which transmit color and other information to the brain. The space between the lens and Retina is filled by a transparent liquid called Viterous gel. Fovea has the highest concentration of cone cells. Cone cells are responsible for seeing color and function best in bright light. | image | teaching_images/human_system_eye_2876.png |
L_1068 | wave interference | DD_0275 | This diagram shows the result of constructive wave interference. The highest point of a waves amplitude is called a crest. The lowest point in amplitude is called a trough. Constructive interference occurs when two waves meet and overlap so that their crests and troughs align. In this image, the crests and troughs of Wave 1 and Wave 2 synchronize. This causes an increase in amplitude. The result is the wave on the right, which has a greater amplitude than Wave 1 and Wave 2. | image | teaching_images/waves_interactions_interference_7681.png |
L_1068 | wave interference | DD_0276 | This diagram shows the results of constructive interference and destructive interference in sound waves. Wave interference is when two waves meet while traveling in opposite directions. The highest point of a waves amplitude is called a crest. The lowest point in amplitude is called a trough. In the example of constructive interference, the crests and troughs of the two waves align. This causes increased wave amplitude when the two waves overlap. In the example of destructive interference, the highest point of amplitude of one wave occurs at the lowest point of the other and cancel each other out. This causes decreased wave amplitude when the two waves overlap. | image | teaching_images/waves_interactions_interference_9298.png |